1. Field of the Invention
The present invention relates to a multi-layered article such as a multi-layered container, a multi-layered parison which is a precursor of a multi-layered container, and a blow molded multi-layered container.
2. Description of the Related Art
In recent years, containers formed of thermoplastic resins are widely used as containers for cosmetics, foods, beverages and the like, from the viewpoints of light weight and safety for breaking. The development of containers formed of a polyethylene terephthalate resin (to be sometimes abbreviated as xe2x80x9cPET resinxe2x80x9d hereinafter) in particular is rapidly advancing owing to improvements in biaxial orientation blow molding technology. However, a container formed of a biaxially oriented thermoplastic polyester resin composed mainly of PET resin does not necessarily have complete performances. That is, when the content to be filled in a container is a food which requires high gas barrier properties of the container, the container formed of PET resin is insufficient in gas barrier properties against oxygen gas and carbon dioxide gas, and therefore, the container formed of PET resin has a defect that the taste of the content is impaired.
For satisfying the above requirement, JP-A-57-128520 (corresponding to U.S. Pat. No. 4,535,901) discloses a method in which an injection-molding apparatus having two injection cylinders for separately plasticizing and melting a thermoplastic polyester resin and an m-xylylene-group-containing polyamide resin (to be sometimes abbreviated as xe2x80x9cMX nylon resinxe2x80x9d hereinafter) which is a thermoplastic gas-barrier resin, respectively, and having a single mold is used, and in one molding cycle, the molten thermoplastic polyester resin is injected, the molten MX nylon resin is injected while the molten thermoplastic polyester resin is being injected, and the injection of the molten thermoplastic polyester resin is continued even after completion of injection of the molten MX nylon resin, to form a parison having a three-layer structure of the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer. The above injection molding method is called a simultaneous-injection molding method.
Further, JP-A-60-240409 (corresponding to EP No. 161625/1985) discloses an injection-molding method similar to the above method, in which, for example, a molten thermoplastic polyester resin and a molten MX nylon resin are injected under specific conditions in the order of the molten thermoplastic resin, the molten MX nylon resin and the thermoplastic polyester resin, to form a parison having a five-layer structure of the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer. The above method is called an alternate-injection molding method.
In recent years, further, a technique is being developed for pelletizing collected containers composed mainly of PET resin and recycling them as a recycled PET resin. When the above recycled PET resin (including a PET resin reclaimed from defective products in the production of parisons and a recycled PET resin once used in the production of parisons) is used to produce parisons for beverage containers, it is required to form a parison having a three-layer structure of the PET resin layer/the recycled PET resin layer/the PET resin layer or a five-layer structure of the PET resin layer/the recycled PET resin layer/the PET resin layer/the recycled PET resin layer/the PET resin layer.
The methods disclosed in the above Japanese Laid-open Patent Publications have enabled the production of multi-layered containers (bottles) having an appearance and mechanical performances equivalent to those of a container formed of a polyethylene terephthalate resin and having greatly improved barrier properties against oxygen gas and carbon dioxide gas, and thus-produced containers are now being used. Meanwhile, there are increasing demands for small-sized bottles in recent years. Since a small-sized bottle has a large surface area relative to a unit internal volume, the loss of carbon dioxide gas contained in a content generally increases, and oxygen gas permeates the contents to affect it to a greater degree. Small-sized bottles are therefore inevitably required to have higher gas-barrier properties.
Conventionally, when a multi-layered molded article (e.g., a multi-layered parison as a precursor of a multi-layered container) formed of two or more resins is produced by means of two or more injection cylinders, there is used an injection molding apparatus having a mold provided with a cavity and having two or more injection cylinders. For example, in an injection molding apparatus having two injection cylinders, resin-flow-passages (a first resin-flow-passage in which a first molten resin flows and a second resin-flow-passage in which a second molten resin flows) connecting the insides of the injection cylinders to the cavity are structured so as to meet with each other in a junction portion in the upstream of a gate portion opened to the cavity. Portions of the first and second resin-flow-passages positioned within the mold have a hot runner structure. Further, portions of the first and second resin-flow-passages upstream to the junction portion generally have the structure of a multiple tube. A screw provided in each injection cylinder is generally structured so as to move back when a pressure is exerted from the resin-flow-passage in any case other than the cases of injection of the molten resin and application of a dwell pressure, so that the molten resin in each resin-flow-passage flows back into each injection cylinder.
A multi-layered container (bottle) formed by biaxially stretch-blow molding a parison having the three-layer structure of PET resin layer/MX nylon resin layer/PET resin layer or the five-layer structure of PET resin layer/MX nylon resin layer/PET resin layer/MX nylon resin layer/PET resin layer has a problem that it is liable to undergo interlayer separation (delamination) when an impact is exerted thereon or when a sharp change occurs in internal pressure after carbonate beverage is filled therein. Further, when a multi-layered container (bottle) having an extremely bend portion is produced by a biaxially stretch-blow molding method, there is another problem that the bend portion is liable to undergo interlayer separation.
For example, JP-A-56-130351 discloses a method of improving the interlayer separation strength. It is described that the above method enables the production of a multi-layered article having high interlayer separation strength by forming an adhesive layer having a specific structure. Impractically, however, the method disclosed in the above Japanese Laid-open Patent Publication requires three injection molding apparatus, and at least there resins are required. Further, JP-A-57-128516 discloses a method of improving the interlayer separation strength, in which the injection of a molten resin for constituting the outermost layer (outer surface and inner surface) is completed before a resin for constituting no outermost layer is cooled to solidness, whereby each layer is brought into an amorphous state. However, the above method is not fully satisfactory for improving the interlayer separation strength.
As compared with a multi-layered container (bottle) having an MX nylon resin layer which extends from its body portion only to its neck portion, a multi-layered container having an MX nylon resin layer which extends from its body portion up to its spout or closure portion through its neck portion has improved barrier properties against oxygen gas and carbonate gas. Since, however, the spout portion is in a non-stretched state, the spout portion is whitened due to water absorption with the lapse of time (i.e., spherulite is formed), which is undesirable in appearance. Further, since gas-barrier resins including the MX nylon resin has a refractive index different from the refractive index of a thermoplastic polyester resin, the ending portion of the gas-barrier resin layer in a multi-layered container is visually recognized as a line, which is clearly observed. That is, the boundary, for example, of the PET resin layer/MX nylon resin layer is clearly observed, which is undesirable in appearance. Moreover, interlayer separation is liable to occur in the above boundary.
In the injection molding apparatus having the above structure, when a first molten resin for forming the outermost layer of the multi-layered article is injected into the cavity through the first resin-flow-passage for completely filling the cavity with the first and second molten resins, the first molten resin flowing along the first resin-flow-passage flows into the second resin-flow-passage. In this case, the inflow of the first molten resin is not constant. As a result, the amount of the first molten resin injected into the cavity is destabilized. Further, during the first injection of the first molten resin, the second molten resin present in the second resin-flow-passage near the junction portion and the first molten resin are injected into the cavity together in a state of a mixture of these resins. This therefore causes a problem that the second resin which is not to compose the outermost layer of the multi-layered article comes to exist on the outermost layer surface.
For preventing the above flow of the first molten resin into the second resin-flow-passage, a prior art uses a hydraulic shut-off valve provided in a nozzle portion of the injection cylinder which is for injecting the second molten resin. Only during the injection of the second molten resin, the shut-off valve is opened, and in any other case, the shut-off valve is closed, whereby the flowing of the first molten resin into the second resin-flow-passage is prevented.
JP-A-61-206612 (corresponding to U.S. Pat. No. 4,657,496) discloses a hot liner mold for injection-molding, which has a first resin-flow-passage 11 and a second resin-flow-passage 12, the second resin-flow-passage 12 being provided with a check valve 13. It is said that when a first resin material A is injected, a cavity 22 is completely filled with the resin but that since the second resin-flow-passage 12 is provided with the check valve 13, a second resin material B flows back due to the first resin material A in no case.
When the flow of a molten resin is controlled by means of the shut-off valve, the flowing of the first molten resin into the second resin-flow-passage can be prevented. However, this causes the following problem. During the first injection of the first molten resin, the first molten resin and the second molten resin are mixed in the vicinity of the junction portion of the resin-flow-passages, or the second molten resin which is not in an injected state is taken into the first molten-resin which is being injected. As a result, the second molten resin present near the junction portion flows into the cavity, and the second resin comes to exist on the surface of the multi-layered article. That is, there is a problem that the second resin which is not to compose the outermost layer of the multi-layered article comes to exist on the outermost layer surface.
It is an object of the present invention to provide a multi-layered article which is formed of at least two resins and has resin layers of these resins laminated, which has an excellent appearance and is free from the occurrence of interlayer separation (delamination), and which is structured such that the resin which is not to compose the outermost layer of the multi-layered article can be reliably prevented from coming to exist on the outermost layer surface thereof, in other words, which is structured such that the resin which is not to compose the outermost layer of the multi-layered article is reliably encapsulated, sealed or blocked with a resin layer composing the outermost layer of the multi-layered article.
The multi-layered article according to a first aspect of the present invention for achieving the above object is a multi-layered article having a first portion constituted of laminated three resin layers and a second portion extending from the first portion,
the first portion being constituted mainly of consecutively laminated resin layers composed of a first resin layer formed of a first resin, a second resin layer formed mainly of a second resin and a third resin layer formed of the first resin,
the second portion being constituted of resin layers extending from the first resin layer and the third resin layer which constitute the first portion,
the first resin layer constituting the outer surface layer of the multi-layered article, the third resin layer constituting the inner surface layer of the multi-layered article which inner surface layer is opposed to said outer surface layer,
the second resin layer being encapsulated with the first resin layer and the third resin layer, and
the second resin layer having a thickness which decreases towards the second portion, and being discontinued, in a region of the first portion in the vicinity of the second portion.
The above region of the first portion in the vicinity of the second portion will be sometimes simply referred to as xe2x80x9cfirst portion regionxe2x80x9d hereinafter.
The multi-layered article according to the first aspect of the present invention can be essentially molded using any type of an injection molding apparatus, but is preferably molded using an injection molding apparatus which comprises;
(a) a mold having a cavity block provided with a cavity and a hot runner block,
(b) a first injection cylinder for injecting a first molten resin and a second injection cylinder for injecting a second molten resin,
(c) a first resin-flow-passage for connecting an inside of the first injection cylinder and the cavity, and
(d) a second resin-flow-passage for connecting an inside of the second injection cylinder and the cavity,
the injection molding apparatus having a structure in which;
those portions of the first and second resin-flow-passages which are located within the mold are provided in the hot runner block, and
the first resin-flow-passage and the second resin-flow-passage meet with each other in a junction portion upstream to a gate portion opened to the cavity,
the injection molding apparatus being provided with back flow means for letting the first molten resin in the first resin-flow-passage flow into the second resin-flow-passage after the second molten resin is injected into the cavity through the second resin-flow-passage, and
the back flow means being operable with a pressure which the first molten resin in the first resin-flow-passage exerts on the second molten resin in the second resin-flow-passage.
Preferably, the first portion is constituted mainly of consecutively laminated resin layers composed of the first resin layer and the third resin layer which are formed of the first molten resin injected from the first injection cylinder into the cavity through the first resin-flow-passage and the gate portion, and the second resin layer which is formed of the second molten resin injected from the second injection cylinder into the cavity through the second resin-flow-passage and the gate portion, and
the above first portion region is formed of the first molten resin which has flowed into the second resin-flow-passage and the second molten resin from the second injection cylinder. The thus-structured multi-layered article will be referred to as xe2x80x9cmulti-layered article according to the second aspect of the present inventionxe2x80x9d for convenience.
In the multi-layered article according to the first aspect of the present invention, including the multi-layered article according to the second aspect of the present invention, the first portion region has a discontinuity. That is, the first portion region is formed of the second resin and the first resin, which are in a crudely mixed state, and the first portion region is constituted of a portion the second resin occupies and the balanced portion the first resin occupies. The first portion is constituted mainly of consecutively laminated resin layers composed of the first resin layer formed of the first resin, the second resin layer formed mainly of the second resin and the third resin layer formed of the first resin. The xe2x80x9csecond resin layer formed mainly of the second resinxe2x80x9d as used herein means that the second resin layer is constituted of a portion of the second resin layer formed of the second resin and a portion of the second resin layer formed of the second resin and the first resin. Further, the xe2x80x9cconstituted mainly of consecutively laminated resin layersxe2x80x9d as used herein means that there is included a case where part of the first portion is constituted of only the first resin layer and the third resin layer which are formed of the first resin.
The multi-layered article according to the first aspect of the present invention, including the second aspect of the present invention, includes an embodiment in which the second resin layer is discontinuously present in the first portion region and along the direction toward the second portion, and an embodiment in which the second resin layer is discontinuously present in the first portion region and along the direction which is at right angles with the direction toward the second portion and which is at right angles with the thickness direction of the multi-layered article. Further, it includes an embodiment in which the second resin layer is discontinuously present in the first portion region and along the direction toward the second portion and along the direction which is at right angles with the direction toward the second portion and is at right angles with the thickness direction of the multi-layered article.
The multi-layered article according to a third aspect of the present invention for achieving the above object is a multi-layered article having a first portion constituted of laminated five resin layers, a second portion extending from the first portion and a third portion extending from the second portion,
the first portion being constituted mainly of consecutively laminated resin layers composed of a first resin layer formed of a first resin, a second resin layer formed of a second resin, a third resin layer formed of the first resin, a fourth resin layer formed of the second resin and a fifth resin layer formed of the first resin,
the second portion being constituted mainly of a first-resin-layer extension layer extending from the first resin layer constituting the first portion, a fifth-resin-layer extension layer extending from the fifth resin layer constituting the first portion, and a second-resin-layer/fourth-resin-layer extension layer mainly extending from the second resin layer and the fourth resin layer constituting the first portion, the third portion being constituted of resin layers extending from the first-resin-layer extension layer and the fifth-resin-layer extension layer constituting the second portion,
the first resin layer and the first-resin-layer extension layer constituting the outer surface layer of the multi-layered article, the fifth resin layer and the fifth-resin-layer extension layer constituting the inner surface layer of the multi-layered article which inner surface layer is opposed to said outer surface layer,
the second resin layer being encapsulated with the first resin layer and the third resin layer,
the fourth resin layer being encapsulated with the fifth resin layer and the third resin layer,
the second-resin-layer/fourth-resin-layer extension layer being encapsulated with the first-resin-layer extension layer and the fifth-resin-layer extension layer, and
the second-resin-layer/fourth-resin-layer extension layer having a thickness which decreases toward the third portion, and being discontinued, in a region of the second portion in the vicinity of the third portion.
The above region of the second portion in the vicinity of the third portion will be sometimes simply referred to as xe2x80x9csecond portion regionxe2x80x9d hereinafter.
The multi-layered article according to the third aspect of the present invention can be essentially molded using any type of an injection molding apparatus, but is preferably molded using an injection molding apparatus which comprises;
(a) a mold having a cavity block provided with a cavity and a hot runner block,
(b) a first injection cylinder for injecting a first molten resin and a second injection cylinder for injecting a second molten resin,
(c) a first resin-flow-passage for connecting an inside of the first injection cylinder and the cavity, and
(d) a second resin-flow-passage for connecting an inside of the second injection cylinder and the cavity,
the injection molding apparatus having a structure in which;
those portions of the first and second resin-flow-passages which are located within the mold are provided in the hot runner block, and
the first resin-flow-passage and the second resin-flow-passage meet with each other in a junction portion upstream to a gate portion opened to the cavity,
the injection molding apparatus being provided with back flow means for letting the first molten resin in the first resin-flow-passage flow into the second resin-flow-passage after the second molten resin is injected into the cavity through the second resin-flow-passage,
the back flow means being operable with a pressure which the first molten resin in the first resin-flow-passage exerts on the second molten resin in the second resin-flow-passage.
Preferably, the first portion is constituted mainly of consecutively laminated resin layers composed of the first resin layer, the third resin layer and the fifth resin layer which are formed of the first molten resin injected from the first injection cylinder into the cavity through the first resin-flow-passage and the gate portion, and the second resin layer and the fourth resin layer which are formed of the second molten resin injected from the second injection cylinder into the cavity through the second resin-flow-passage and the gate portion, and
the above second portion region is formed of the first molten resin which has flowed into the second resin-flow-passage and the second molten resin from the second injection cylinder. The thus-structured multi-layered article will be referred to as xe2x80x9cmulti-layered article according to the fourth aspect of the present inventionxe2x80x9d for convenience.
In the multi-layered article according to the third aspect of the present invention, including the fourth aspect of the present invention, the second-resin-layer/fourth-resin-layer extension layer has a discontinuity in the second portion region. That is, the second portion region is formed of the second resin and the first resin, which are in a crudely mixed state, and the second portion region is constituted of a portion the second resin occupies and the balanced portion the first resin occupies. The first portion is constituted mainly of consecutively laminated resin layers composed of the first resin layer formed of the first resin, the second resin layer formed of the second resin, the third resin layer formed of the first resin, the fourth resin layer formed of the second resin and the fifth resin layer formed of the first resin. The xe2x80x9cconstituted mainly of consecutively laminated resin layersxe2x80x9d means that there is included a case where part of the first portion is constituted of the first resin layer, the third resin layer and the fifth resin layer which are formed of the first resin, and the fourth resin layer which is formed of the second resin. Further, the second portion is constituted mainly of the first-resin-layer extension portion extending from the first resin layer constituting the first portion, the fifth-resin-layer extension layer extending from the fifth resin layer constituting the first portion, and the second-resin-layer/fourth-resin-layer extension layer extending from the second resin layer and the fourth resin layer which constitute the first portion. The xe2x80x9cconstituted mainly of the second-resin-layer/fourth-resin-layer extension layer extending from the second resin layer and the fourth resin layer which constitute the first portionxe2x80x9d means that the second-resin-layer/fourth-resin-layer extension layer is constituted of a portion of the second-resin-layer/fourth-resin-layer extension layer formed of the second resin and a portion of the second-resin-layer/fourth-resin-layer extension portion formed of the second resin and the first resin.
The multi-layered article according to the third aspect of the present invention, including the fourth aspect of the present invention, includes an embodiment in which the second-resin-layer/fourth-resin-layer extension layer is discontinuously present in the second portion region and along the direction toward the third portion, and an embodiment in which the second-resin-layer/fourth-resin-layer extension layer is discontinuously present in the second portion region and along the direction which is at right angles with the direction toward the third portion and which is at right angles with the thickness direction of the multi-layered article. Further, it includes an embodiment in which the second-resin-layer/fourth-resin-layer extension layer is discontinuously present in the second portion region and along the direction toward the third portion and along the direction which is at right angles with the direction toward the third portion and is at right angles with the thickness direction of the multi-layered article.
In the multi-layered article according to the present invention, the first resin is at least one resin selected from the group consisting of thermoplastic polyester resins such as polyethylene terephthalate and polyethylene-2,6-naphthalate (PEN); a thermoplastic copolyester resin; a polyolefin resin; an aliphatic polyamide resin; a polycarbonate resin; a polyacrylonitrile resin; a polyvinyl chloride resin; and a polystyrene resin. Of these, thermoplastic polyester resins are preferred. Further, a blend prepared by blending two or more resins, e.g., a blend prepared by blending a polyethylene terephthalate resin and a polyethylene-2,6-naphthalate resin may be used as required.
The above polyethylene terephthalate generally refers to a polyester formed of a dicarboxylic acid moiety at least 80 mol %, preferably at least 90 mol %, of which is from terephthalic acid and a diol moiety at least 80 mol %, preferably at least 90 mol %, of which is from ethylene glycol. The balance of the acid component thereof is selected from isophthalic acid, diphenyl ether-4,4-dicarboxylic acid, naphthalene-1,4, or 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane-1,10-decarboxylic acid and hexahydroterephthalic acid. The balance of the glycol component is selected from propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, cyclohexanedimethanol and 2,2-bis(4-hydroxyethoxyphenyl)propane. Further, there may be used a polyester resin containing p-hydroxybenzoic acid as a hydroxy acid.
Further, the polyethylene-2,6-naphthalate may contain other ester-forming units in an amount of 20 mol % or less, preferably 10 mol % or less in addition to ethylene-2,6-naphthalate. A dicarboxylic acid for forming the xe2x80x9cotherxe2x80x9d ester-forming units preferably includes aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4xe2x80x2-diphenylcarboxylic acid and 3,4xe2x80x2-diphenylcarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid and dodecanedioic acid; and aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, decalindicarboxylic acid and tetralindicarboxylic acid. A diol for forming the xe2x80x9cotherxe2x80x9d ester-forming units preferably includes aliphatic glycols such as propylene glycol, trimethylene glycol, diethylene glycol and 1,4-butanediol; aliphatic glycols such as 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol and 1,6-cyclohexanediol; and aromatic glycols such as bisphenol A. The above polyethylene-2,6-naphthalate may have a molecule whose terminal is blocked with a small amount of a monofunctional compound such as benzoic acid, benzoylbenzoic acid, benzyloxybenzoic acid or methoxypolyethylene glycol. Further, it may contain a very small amount of a polyfunctional compound such as glycerin, trimesic acid or pentaerythritol.
The intrinsic viscosity of the above thermoplastic polyester resin is properly at least 0.40, preferably 0.50 to 1.4. When the above intrinsic viscosity is less than 0.40, an obtained multi-layered article (e.g., multi-layered bottle) is poor in mechanical strength, and further, it is difficult to produce, e.g., a multi-layered article in an amorphous and transparent state. The xe2x80x9cintrinsic viscosity (xcex7)xe2x80x9d is a viscosity measured at 30xc2x0 C. using mixed solvents of phenol/tetrachloroethane=6/4 (weight ratio).
The above thermoplastic copolyester resin refers to a thermoplastic copolyester resin obtained by copolymerizing at least one acid component and at least one diol component. The acid component is selected from terephthalic acid, isophthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid. The diol component is selected from ethylene glycol, propylene glycol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,3-bis(2-hydroxyethoxy)benzene, and 1,4-bis(2-hydroxyethoxy)benzene. The above thermoplastic copolymer resin may be used with other thermoplastic polyester resin as required.
In the multi-layered article according to the present invention, the second resin is at least one resin selected from the group consisting of a thermoplastic resin having gas barrier properties (gas-barrier resin), a recycled polyethylene terephthalate resin (including a polyethylene terephthalate resin reclaimed from a resin once used in the production of multi-layered articles) and a colored polyethylene terephthalate resin.
The above gas-barrier resin is preferably at least one resin selected from the group consisting of a m-xylylene-group-containing polyamide resin (MX nylon resin), a saponification product of an ethylene-vinyl acetate copolymer resin, a polyacrylonitrile resin and a polyvinylidene chloride resin. Of these resins, MX nylon resin is particularly preferred.
The above MX nylon resin refers to a polymer containing diamine component including m-xylylenediamine of at least 70 mol % and dicarboxylic acid component including adipic acid of at least 70 mol %. Diamines other than m-xylylenediamine are not specifically limited and may include paraxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, tetramethylenediamine, hexamethylenediamine, nonamethylenediamine, 2-methyl-1,5-pentanediamine, etc. Dicarboxylic acids other than adipic acid are not specifically limited and may include suberic acid, azelaic acid, sebacic acid, 1,10-decanedicarboxylic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, etc. The polyamide used may contain a small amount of a monoamine and a monocarboxylic acid added during the condensation polymerization as a molecular weight modifier. The above polymers may contain polymers such as nylon 6, nylon 66, nylon 610 or nylon 11.
The relative viscosity of the MX nylon resin is properly at least 1.5, preferably 2.0 to 4.0. The relative viscosity (xcex7rel) is a viscosity measured at 25xc2x0 C. under a condition of resin 1 gram/96% sulfuric acid 100 ml.
In the multi-layered article according to the present invention, a combination of a thermoplastic polyester resin, particularly, a polyethylene terephthalate resin (PET resin), with MX nylon resin is most preferred, since these resins are excellent in all of transparency, mechanical strength, injection moldability and stretch blow moldability. Further, since these two resins have similar thermal properties, it is easy to determine molding temperature conditions. In this case, preferably, the polyethylene terephthalate resin and the MX nylon resin have melt viscosity values close to each other. For example, when a polyethylene terephthalate resin having an intrinsic viscosity of 0.7 to 0.8 is used, it is desirable to use an MX nylon resin having a relative viscosity of approximately 2.7. When other gas-barrier resin is used, preferably, the gas-barrier resin has a melt viscosity close to the melt viscosity of the polyethylene terephthalate resin.
When PET resin and MX nylon resin are combined, in the second resin layer or the second-resin-layer/fourth-resin-layer extension layer, the second resin which is dispersed like islands or is extending in an acicular form can be observed by staining the MX nylon resin with iodine tincture. Otherwise, they can be observed by placing the first portion or the second portion between two polarizers arranged in Crossed Nicols, i.e., in directions at right angles with each other.
In the multi-layered article according to the present invention, further, the first resin, the second resin or each of resins forming a multi-layered article may contain a colorant, an ultraviolet absorbent, an antistatic agent, an antioxidant, a lubricant, a nucleating agent, a bactericide and a fungicide.
In the injection molding apparatus used for the production of the multi-layered article according to the second or fourth aspect of the present invention, the term xe2x80x9cupstreamxe2x80x9d means a position on the injection cylinder side, xe2x80x9cdownstreamxe2x80x9d means a position on the cavity side, and these terms will be used in these sense hereinafter.
The multi-layered article according to the second aspect of the present invention can be manufactured by the steps of;
(A) injecting the first molten resin prepared in the first injection cylinder into the cavity through the first resin-flow-passage,
(B) injecting the second molten resin prepared in the second injection cylinder into the cavity through the second resin-flow-passage during the injection of the first molten resin, and
(C) after completion of injection of the second molten resin, letting the first molten resin in the first resin-flow-passage flow into the second resin-flow-passage on the basis of operation of the back flow means during the injection of the first molten resin or after completion of injection of the first molten resin. The above injection molding method is called a simultaneous-injection molding method. In the above step (B), the injection amount of the first molten resin per unit time is preferably greater than the injection amount of the second molten resin per unit time.
FIGS. 17, 18 and 19 show changes of injection rates, etc., with the elapse of time in the method of injection molding the multi-layered article according to the second aspect of the present invention. In FIGS. 17 to 22, xe2x80x9cclosed statexe2x80x9d in xe2x80x9cstate of back flow meansxe2x80x9d means that the inside of the second injection cylinder and the cavity are maintained in a non-communicated state on the basis of operation of the back flow means, and xe2x80x9copen statexe2x80x9d means that the inside of the second injection cylinder and the cavity are maintained in a communicated state by means of the back flow means. The xe2x80x9cback flowxe2x80x9d means the following state. That is, the back flow means is being operated with a pressure which the first molten resin in the first resin-flow-passage exerts on the second molten resin in the second resin-flow-passage, so that the first molten resin in the first resin-flow-passage flows into the second resin-flow-passage, and as a result, the second molten resin flows toward the second injection cylinder. When the first molten resin in the first resin-flow-passage is allowed to flow into the second resin-flow-passage on the basis of operation of the back flow means after the completion of injection of the first molten resin, specifically, a dwell pressure is applied with the first injection cylinder, and after completion of injection of the first molten resin, the back flow means is operated to allow the first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage (see FIG. 19). When the first molten resin in the first resin-flow-passage begins to flow into the second resin-flow-passage on the basis of operation of the back flow means during the injection of the first molten resin, the inflow of the first molten resin into the second resin-flow-passage may be completed during the injection of the first molten resin (see FIG. 17), concurrently with completion of injection of the first molten resin or during the application of a dwell pressure after completion of injection of the first molten resin (see FIG. 18).
The multi-layered article according to the fourth aspect of the present invention can be manufactured by the steps of;
(A) injecting the first molten resin prepared in the first injection cylinder into the cavity through the first resin-flow-passage and then discontinuing the injection of the first molten resin,
(B) injecting the second molten resin prepared in the second injection cylinder into the cavity through the second resin-flow-passage and then terminating the injection of the second molten resin, and then,
(C) injecting the first molten resin prepared in the first injection cylinder into the cavity through the first resin-flow-passage and letting the first molten resin in the first resin-flow-passage flow into the second resin-flow-passage on the basis of operation of the back flow means during the injection of the first molten resin or after completion of injection of the first molten resin. The above method is called an alternate-injection molding method.
FIGS. 20, 21 and 22 show changes of injection rates, etc., with the lapse of time in the method of injection molding the multi-layered article according to the fourth aspect of the present invention. When the first molten resin in the first resin-flow-passage is allowed to flow into the second resin-flow-passage on the basis of operation of the back flow means after completion of injection of the first molten resin, specifically, a dwell pressure is applied with the first injection cylinder, and after the completion of injection of the first molten resin, the back flow means is operated to allow the first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage (see FIG. 22). When the first molten resin in the first resin-flow-passage begins to flow into the second resin-flow-passage on the basis of operation of the back flow means during the injection of the first molten resin, the inflow of the first molten resin into the second resin-flow-passage may be completed during the injection of the first molten resin (see FIG. 20), concurrently with the completion of injection of the first molten resin or during the application of a dwell pressure after completion of injection of the first molten resin (see FIG. 21).
In the injection molding apparatus for injection molding the multi-layered article according to the second or fourth aspect of the present invention, preferably, the back flow means (counter-flow means) allows a constant amount of the first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage. Preferably, further, when the second molten resin is being injected into the cavity through the second resin-flow-passage and after the injection of the second molten resin is completed, the inside of the second injection cylinder and the cavity are brought into a communicated state by means of the back flow means, and after a predetermined amount of the first molten resin in the first resin-flow-passage is allowed to flow into the second resin-flow-passage, the inside of the second injection cylinder and the cavity are brought into a non-communicated state on the basis of operation of the back flow means. xe2x80x9cPredetermined amountxe2x80x9d and xe2x80x9cconstant amountxe2x80x9d have a relationship of (predetermined amount)xe2x89xa6(constant amount). Alternatively, preferably, when the second molten resin is being injected into the cavity through the second resin-flow-passage and after the injection of the second molten resin is completed, the inside of the second injection cylinder and the cavity are brought into a communicated state by means of the back flow means, and after the first molten resin in the first resin-flow-passage begins to flow into the second resin-flow-passage, the inside of the second injection cylinder and the cavity are brought into a non-communicated state on the basis of operation of the back flow means. The back flow means is preferably provided in that part of the second resin-flow-passage which is between the junction portion of the first and second resin-flow-passages and the second injection cylinder. In this case, particularly preferably, the back flow means is provided between the nozzle portion of the second injection cylinder and the mold, or in the nozzle portion of the second injection cylinder. Preferably, the back flow means is a back flow control valve (a counter-flow control valve) from the viewpoint of allowing a constant amount of the first molten resin to flow into the second resin-flow-passage and from the viewpoint of structural simplification. The back flow control valve includes a ball-type back flow control valve and a sliding valve-type back flow control valve.
In the multi-layered article according to the second or fourth aspect of the present invention, the volume of the first molten resin which is allowed to flow into the second resin-flow-passage is 5 to 50%, preferably 5 to 35%, more preferably 5 to 25%, based on the volume of the cavity. When the volume of the first molten resin which is allowed to flow into the second resin-flow-passage is less than 5% based on the volume of the cavity, it may be difficult to prevent the resin which is not to compose the outermost layer of the multi-layered article from coming to exist on the outermost layer surface thereof. Although depending upon injection conditions, the resin layers composing the layers of the multi-layered article undergo turbulence since the first molten resin is allowed to flow into the second resin-flow-passage. For reliably preventing the above turbulence, the volume of the first molten resin which is allowed to flow into the second resin-flow-passage is preferably 35% or less, particularly preferably, 25% or less, based on the volume of the cavity. When the above amount of the first molten resin exceeds 50% based on the volume of the cavity, the resin layers composing the layers of the multi-layered article may have a turbulence which is a practical problem in many cases.
In the multi-layered article according to the first aspect of the present invention, including the second aspect of the present invention, for reliably decreasing the thickness of the second resin layer in the first portion region toward the second portion, it is preferred to gradually increase the injection rate of the second molten resin without sharply increasing it in the beginning of the injection, as shown in FIG. 23A. In the multi-layered article according to the third aspect of the present invention, including the fourth aspect of the present invention, for reliably decreasing the thickness of the second-resin-layer/fourth-resin-layer extension layer in the second portion region toward the third portion, it is preferred to gradually increase the injection rate of the second molten resin without sharply increasing it in the beginning of the injection, as shown in FIG. 23B.
Further, it is preferred to bring the melt viscosity of the first resin and the melt viscosity of the second resin into values which are as close to each other as possible, and the first resin/second resin melt viscosity ratio is preferably 0.5 to 2. When the melt viscosity of the first resin is too high relative to the melt viscosity of the second resin, it is sometimes difficult to gradually decrease the thickness of the second resin layer in the first portion region in the multi-layered article according to the first aspect of the present invention, including the second aspect of the present invention, or it is sometimes difficult to gradually decrease the thickness of the second-resin-layer/fourth-resin-layer extension layer in the second portion region in the molded article according to the third aspect of the present invention, including the fourth aspect of the present invention. When the melt viscosity of the first resin is too low relative to the melt viscosity of the second resin, it is possible to gradually decrease the thickness of the second-resin-layer/fourth-resin-layer extension layer in the second portion region, while there is sometimes a problem that the ending portion of the third resin layer formed from the first molten resin comes to be roundish.
The multi-layered article according to the first to fourth aspects of the present invention may have any structure or form, and it includes a multi-layered container, a parison as a precursor for forming a multi-layered container (bottle) and a blow molded multi-layered container. Further, the multi-layered article includes a bumper and a door handle for an automobile. Further, the multi-layered article also includes a multi-layered article formed by combining a plurality of resins for imparting it with different functions such as strength, an appearance and the like, on the basis of a multi-layer forming technique. It is sometimes difficult to identify the outer surface layer and the inner surface layer of a multi-layered article having some form. In this case, a first surface can be considered the outer surface layer and a second surface which is opposed to the first surface can be considered the inner surface layer.
In the first portion region of the multi-layered article according to the first aspect of the present invention, including the second aspect of the present invention, the thickness of the second resin layer decreases toward the second portion. In the second portion region of the multi-layered article according to the third aspect of the present invention, including the fourth aspect of the present invention, the second-resin-layer/fourth-resin-layer extension layer decreases toward the third portion. As a result, the clear observation of these regions comes to be not easy, and there can be overcome the problem of prior art in which, for example, the boundary of a PET resin layer/MX nylon resin layer is clearly observable. Further, the ratio of the third portion of the multi-layered article can be relatively decreased, and the multi-layered article as a whole can be also further improved in gas barrier properties.
Further, in the first portion region of the multi-layered article according to the first aspect of the present invention, including the second aspect of the present invention, the second resin layer is discontinuously present. In the second portion region of the multi-layered article according to the third aspect of the present invention, including the fourth aspect of the present invention, the second-resin-layer/fourth-resin-layer extension layer is discontinuously present. The interlayer separation (delamination) can be therefore improved. Further, there can be also overcome the problem that the multi-layered article comes to be whitened with the lapse of time.
Moreover, in the first portion region of the multi-layered article according to the first aspect of the present invention, including the second aspect of the present invention, the second resin layer is encapsulated with the first resin layer and the third resin layer. In the second portion region of the multi-layered article according to the third aspect of the present invention, including the fourth aspect of the present invention, the second resin layer is encapsulated with the first resin layer and the third resin layer, the fourth resin layer is encapsulated with the fifth resin layer and the third resin layer, and the second-resin-layer/fourth-resin-layer extension layer is encapsulated with the first-resin-layer extension layer and the fifth-resin-layer extension layer. There is therefore overcome the problem that the resin layer which is not to constitute the outermost layer appears on the outermost layer surface.
The multi-layered article according to the second or fourth aspect of the present invention is manufactured using the injection molding apparatus provided with the back flow means for allowing the first molten resin in the first resin-flow-passage to flow into the second resin-flow-passage. When the first molten resin is injected into the cavity, therefore, the first molten resin (which has flowed into the second resin-flow-passage in a previous molding cycle) has been present in that portion of the second resin-flow-passage which is near the junction portion of the resin-flow-passages. Therefore, there can be prevented a phenomenon that the first molten resin to be injected is mixed with the second molten resin in the second resin-flow-passage in the vicinity of the junction portion, and there can be prevented a phenomenon that the second molten resin which is not in an injected state is taken into the first molten resin which is being injected. As a result, there can be reliably prevented a problem that the second resin comes to exist on the surface of the multi-layered article.